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FIX k A PRo9LEM ASSESSMENT REPORT Moore Petroleuh, Inc. 1399 E. YOGMite Avenue, Manteca, CA NGA Project No. 10.90.480 Page 4 3.0 RESULTS OF RECENT INVESTIGATION ACTIVITIES 3.1 Drilling and soil Sampling On June 12, 1990, a representative of NGA supervised the abandonment of monitoring well MW-1. This well had been damaged during the removal of USTs at the site in September, 1989. MW-1 was abandoned using a CME-55 drilling rig and 8-inch-diameter hollow-stem augers. The proposed abandonment procedure consisted of over-drilling the PVC well casing using hollow-stem augers, removal of the well casing from the borehole, and cementing the borehole with a bentonite/cement grout to the ground surface. After over-drilling to a depth of about ten feet it was discovered that the well casing was no longer inside the hollow-stem augers. At that time, all augers were removed from the borehole and an unsuccessful attempt was made to locate the well casing within the borehole. After consulting with, and receiving approval from, the on-site representative from the San Joaquin Public Health service, well abandonment was completed by drilling to the completion depth of the well and cementing the borehole to the surface with a cement/bentonite grout. On June 21, 1990, monitoring well MW-1A was installed at a location approximately ten feet from the original location of MW-1 (Figure 2) . The soil boring for 14W-1A was advanced using a CME-55 drilling rig utilizing 8-inch-diameter hollow stem augers. samples of subsurface soils were obtained From the soil boring at five foot intervals using a California modified split-spoon sampler. All soil samples were examined in the field by a California Registered geologist and described for color, grain size, moisture content, mineral content, and odor. Soil samples were classified in accordance with the Unified Soil Classification System. All drilling and sampling equipment was cleaned prior to drilling the soil boring using a high-pressure, steam--cleaning apparatus. The split-spoon sampler was cleaned with phosphate-free soap and rinsed with water following the collection of each soil sample. Drill cuttings were placed on plastic and stockpiled on-site. The soil boring log for well MW-1A is presented in Appendix A. 3.2 Monitoring Wall Installatzon gad Development Monitoring well MW-1A was constructed using flush-threaded, two- inch-diameter, schedule 40 PVC blank casing and two-inch-diameter, Schedule 40 PVC well screen -with_0-.010--inch well-slots.---Following--.--- the --Following .the placement of well casing and screen, a sand filter pack, _ extending from the bottom of the well screen to approximately two feet above the top of the well screen, was placed in the annular space between the well screen and borehole.